North Korea's military unleashed its standard fiery threats to greet the start of annual US-South Korean military drills that the North claims are an invasion rehearsal. The North Korean rhetoric today came as top US generals, including Admiral Harry Harris, the commander of US forces in the Pacific, visited South Korea. The US generals were to travel to the site of a contentious US missile defence system in South Korea later on Tuesday. The North's military says it will launch an unspecified "merciless retaliation and unsparing punishment" on the United States over the Ulchi Freedom Guardian drills that began yesterday.North Korea has previously issued similar warlike rhetoric whenever US and South Korean troops conducted major joint exercises. An unprompted direct attack is extremely unlikely because the United States vastly outguns Pyongyang.